1. Field of the Invention
The present invention relates to an IC package testing device for evaluating electrical characteristics of an IC package, particularly BGA (ball grid array), and a method for testing an IC package using the testing device. More particularly, the present invention relates to a handling device and a handling method for properly abutting solder balls of an IC package respectively on a plurality of measurement contact pins provided in a socket in the testing device.
1. Description of the Related Art
In recent years, as the number of pins provided in an IC package increases, BGA has been used more widely. First, a general structure of a BGA will be described. FIG. 1A is a side view of a BGA, and FIG. 1B is a plan view thereof. The BGA 1 is a semiconductor component having a rectangular shape. The BGA 1 is about 5 to 50 mm long along each side and about 0.5 to 3 mm thick. A plurality of solder balls 2 are provided on one surface of the BGA 1. An LSI (large-scale integrated circuit) 3 is buried in the central part of the BGA 1. Each electrode (not shown) of the LSI 3 is connected to a respective one of the solder balls 2 via a respective one of thin lines (not shown) running through the inside of the BGA 1. As a method for mounting the BGA 1 on a printed board (not shown), the surface of the BGA 1 having the solder balls 2 provided thereon is placed on the printed board and the solder balls 2 are melted so that the BGA 1 is integrated into the printed board as a circuit.
As shown in FIG. 1B, the BGA 1 includes a number of solder balls 2 arranged in a grid pattern which extends along the periphery thereof. Each solder ball 2 has a generally hemispherical shape and protrudes from the surface of the BGA 1. Each of the solder balls 2 has a diameter as small as about 0.3 mm. Recently, a single BGA 1 has some hundreds to one thousand or more of the solder balls 2, with a pitch of grid as small as about 0.5 mm. Recently, the degree of integration of an LSI has been increased. Along with that, the number of the solder balls 2 needs to be further increased. Meanwhile, a high-density mounting onto the printed board is also demanded. Therefore, it is difficult to increase the size of the BGA 1 itself. Thus, the density of the array of the solder balls 2 tends to be further increased.
Next, a method for measuring electrical characteristics of the BGA 1 will be described. FIG. 2A through FIG. 2D are cross-sectional views sequentially illustrating the steps of a method for testing electrical characteristics of the BGA 1 using a conventional socket 4p. In general, a jig (hereinafter, referred to as a socket) including a group of contact pins 5p having an array identical to that of the solder balls 2 is used for the measurement. The contact pins 5p can be compressed and expanded by a certain amount. When compressed and expanded, a predetermined spring pressure is applied to the point of contact. As the solder balls 2 are pressed against the tips of the contact pins 5p, the contact pins 5p are electrically connected to the solder balls 2, thereby making it possible to measure various kinds of electrical characteristics of the BGA 1. The contact pins 5p shown in FIG. 2A are, for example, of a type which includes a compression spring (not shown) under each pin, and generates a spring pressure according to the amount of compression thereof.
The steps of the method for measuring electrical characteristics of the BGA 1 will be sequentially described below. First, the BGA 1 is positioned with respect to the socket 4p based on the outer shape of the BGA 1 as shown in FIG. 1B. Thereafter, a suction head 6p sucks onto a surface of the BGA 1 which is opposite to the surface including the solder balls 2, and carries the BGA 1 over the socket 4p. 
Next, as shown in FIG. 2A, the suction head 6p inserts the BGA 1 into the socket 4p. The socket 4p includes many contact pins 5p on the bottom. Each side wall of the socket 4p is formed of two portions, i.e., a tapered section 40 and a straight section 41. The tapered section 40 adjoins the opening of the socket 4p. The side wall of the tapered section 40 is tapered such that it flares upwardly. If the BGA 1 has a square shape as shown in FIG. 1B, the side wall of the tapered section 40 has four tapered sides. The straight section 41 adjoins the bottom of the socket 4p, and has a vertical side wall.
Next, after the suction head 6p carries the BGA 1 to the tapered section 40, suction is ceased so as to release and drop the BGA 1 off from the suction head 6p as shown in FIG. 2B. Then, BGA 1 slides down along the tapered surfaces of the tapered section 40 and into the straight section 41.
As shown in FIG. 2C, each of the solder balls 2 is loaded on a respective one of the contact pins 5p at the bottom of the socket 4p, and the falling down of the BGA 1 is stopped. The shape of the straight section 41 is set to be slightly larger than the outer shape of the BGA 1, thereby making it possible to abut the BGA 1 on the respective contact pins 5p based on the outer shape of the BGA 1.
Next, as shown in FIG. 2D, the suction head 6p is lowered by a predetermined amount so as to press the BGA 1. As a result, the contact pins 5p are pressed down by a certain amount via the BGA 1. Consequently, each of the contact pins 5p is electrically connected to a respective one of the solder balls 2. Thus, using a measuring instrument (not shown) which is connected to each of the contact pins 5p via a cable or the like (not shown), various kinds of electrical characteristics are measured. After the measurement, the suction head 6p is raised while sucking onto the BGA 1 again, and carries the BGA 1 to a predetermined position for the next step to be performed.
However, the conventional IC package testing device and testing method have problems as follows. First of all, the socket has a structural problem. As described above, when the BGA 1 slides down along the tapered section 40 in the opening of the socket 4p, the BGA 1 does not always slides down smoothly. Sometimes, the BGA 1 is stuck halfway through. FIG. 3A is a cross-sectional view showing a case where the BGA 1 is stuck halfway through the tapered section 40. The suction head 6p carries the BGA 1 to a predetermined position within the opening of the socket 4p, and then the suction is ceased so as to drop the BGA 1. However, while the BGA 1 is sliding down off from the suction-head 6p, a part of the BGA 1 is stuck in the tapered section 40, thereby preventing the BGA 1 from properly falling down from the suction head 6p. As shown in FIG. 3B, however, the suction head 6p is lowered by a predetermined amount even in such a state, whereby an excessive amount of external force is applied to the BGA 1 from above, damaging the BGA 1.
Moreover, the force applied by the suction head 6p is also applied to the contact pins 5p. This force is applied not only in the direction along which the contact pins 5p are compressed and expanded (i.e., the vertical direction) but also in the lateral direction. As described above, each of the contact pins 5p can be compressed and expanded due to the compression spring included therein. However, the maximum spring pressure during its compression and expansion is as small as about 10 g, and the size of the tip portion of the contact pin 5p is as small as about xcfx860.3 mm which is about the same as that of the solder ball 2. Thus, the contact pin 5p is a component which is extremely thin and fragile. As a result, when an external force in the lateral direction is applied thereto, the contact pin 5p is easily bent. If even only one contact pin 5p among many is bent and thus can no longer be compressed and expanded smoothly. As a result, the remaining contact pins 5p cannot abut on the solder balls 2, making it impossible to measure the electrical characteristics at all.
Furthermore, even when the BGA 1 successfully slides down the opening of the socket 4p, the solder balls 2 do not always abut on the contact pins 5p in an aligned manner. This is a problem arising from the manufacture of the BGA 1. In particular, although the solder balls 2 are arranged in a grid pattern having a constant pitch, the solder balls 2 are not manufactured based on the outer shape of the BGA 1. Therefore, the array of the solder balls 2 with respect to the outer shape of the BGA 1 often varies from a BGA to another.
FIG. 4A is a side view of a BGA 1e in which the solder balls 2 are out of alignment with respect to the outer shape of the BGA 1e, and FIG. 4B is a plan view thereof. In such a case, the solder balls 2 abut on the respective contact pins 5p while their central axes are out of alignment with each other.
Therefore, when the suction head 6p is lowered by a predetermined amount, a force in the lateral direction is applied to the solder balls 2 via the BGA 1e. As a result, the solder balls 2 may be stripped off from the BGA 1e. Moreover, since this is a lateral a direction force also for the contact pins 5p, the contact pins 5p may be damaged, thereby preventing them from being smoothly compressed and expanded.
When such a defect occurs in a contact pin, the contact pin needs to be replaced. As described above, however, the contact pin is a minute and fragile component. Also, precise positioning is required when attaching the contact pins, and it is also necessary to ensure that all the contact pins are uniformly compressed and expanded. Therefore, such a replacing operation is very difficult to perform, and it is practically impossible for a measurer to replace the defective contact pin by himself/herself. Therefore, conventionally, the entire socket has been replaced. As described above, since the socket is a very expensive component because of its special and precise structure, the replacement of the socket incurs a very high cost. Thus, in a conventional testing device for evaluating electrical characteristics of an IC package such as a BGA, a contact pin thereof is damaged every time the BGA is stuck in the socket section or out-of-alignment occurs between the solder balls and the contact pins, frequently causing the need for replacing the socket. As a result, the running const of this testing device is very expensive.
Furthermore, according to the conventional testing device and the conventional testing method, an electrical resistance between the contact pin and the solder ball becomes unstable. Electrical contact between the contact pin and the solder ball in the measurement of electrical characteristics will be described below. The tip of the contact pin is sharpened like the tip of a needle. The tip of the contact pin abuts on the solder ball, thereby applying a certain level of pressing pressure thereto. As a result, an oxide film formed on the surface of the solder ball is torn, thereby electrically connecting the contact pin to the solder ball. There exist many types of contact pins, for example, a contact pin having a single sharpened tip portion, a contact pin having a plurality of sharpened tip portions, and a contact pin with a tip formed by firmly bundling a number of thin metal wires and cutting the bundled metal wires in a direction perpendicular to the metal wires, with the cut face being used as the tip of the contact pin. The tip of the contact pin formed by bundling the metal wires appears to be flat.
A preferred contacting state between the contact pin and the solder ball is a state where the pressing pressure applied to the contact pin and the solder ball is minimum while the electrical resistance at the point of contact therebetween is minimum. If the pressing pressure applied by the suction head is so weak that the contact pin cannot tear the oxide film on the surface of the solder ball 2, the electrical resistance at the point of contact becomes large, failing to obtain normal measurement values. On the contrary, an excessive pressing pressure is meaningless for measurement because the electrical resistance at the point of contact cannot be smaller than a certain value. By repeating measurement with such an excessive pressing pressure, the contact pin is mechanically damaged in a repeated manner, thereby causing an adverse influence which reduces the lifetime of the fragile contact pin. Therefore, an ideal contacting state is a state in which the pressing pressure is minimum while the contact resistance is minimum, i.e., the state in which the amount of compression of the contact pin is minimum while the contact pin abuts on the solder ball after the oxide film on the surface of the solder ball is torn by the contact pin.
However, according to the conventional testing method, as shown in FIG. 2D, the BGA 1 mounted on the contact pins 5p is pushed down by a certain amount using the suction head 6p placed on the BGA 1. When the suction head 6p is lowered and then stopped, the position of the tip of the suction head 6p is always the same regardless of the thickness of the BGA 1. The thickness of a BGA is generally in a range of about 0.5 to about 3 mm. However, even among the same kind of BGAs, the thicknesses thereof often vary for different manufacturing lots. For example, the thickness of products whose standard thickness is 1 mm may sometimes vary by as much as 0.3 mm. Therefore, according to the conventional method in which the suction head 6p is lowered until it reaches a certain height for any BGA to be measured, the amount of compression of the contact pins 5p varies for various BGAs. In an extreme case, the contact pin 5p may not be compressed at all. Thus, according to the conventional measurement method, it is impossible to absorb the variation in the thickness among BGAs and to make the contact pins 5p respectively abut on the solder balls 2 with a uniform and optimal pressing pressure regardless of the thickness of the BGA.
An object of the present invention is to provide an IC package testing device and a method for testing an IC package using such an IC package testing device in which: an IC package is not stuck in a socket section, thereby always making solder balls of the IC package respectively abut on contact pins in the socket section in an aligned manner; and the solder balls are respectively abutted on the contact pins with an optimal load regardless of the thickness of the IC package, thereby making it possible to extend the lifetime of the contact pins and to measure electrical characteristics of the IC package in a highly accurate and highly efficient manner.
An IC package testing device according to the present invention comprises: a measuring unit having a socket including contact pins which contact on solder balls in an IC package for measuring electrical characteristics of the IC package; a camera unit for imaging a positional pattern of the solder balls in the IC package; an image recognition unit which recognizes an image obtained by the camera unit, processes the image, and obtains a positional pattern data of the solder balls; a first memory unit for storing the pattern data of the solder balls; a second memory unit for storing a positional pattern data of the contact pins in the socket; an adjusting unit for adjusting a position of the IC package so as to align the positional pattern of the solder balls with the positional pattern of the contact pins at a positioning section; and a carrier unit for holding the IC package which has been adjusted the position thereof at the positioning section, and carrying it to the socket and contacting the solder balls on the contact pins while holding the IC package.
According to the present invention, the position of the IC package is adjusted using the adjusting unit in association with the positions of the solder balls in the IC package and the positions of the contact pins in the socket. As a result, the positions of the solder balls can be accurately controlled, thereby making it possible to abut the solder balls on the contact pins in an aligned manner. Furthermore, the solder balls are respectively abutted on the contact pins while the carrier unit is holding the IC package, thereby preventing the IC package from being stuck.
The IC package testing device of the present invention may comprise: a plurality of pilot pins which are provided in the socket and have a fixed positional relationship with the contact pins; a socket calibration jig including a plurality of pilot holes which are fitted around the pilot pins and a plurality of image recognition marks which have a fixed positional relationship with the pilot holes; another camera unit for imaging the image recognition marks; and another image recognition unit which recognizes an image obtained by the camera unit, processes the image, and obtains a positional data of the image recognition marks and the positional pattern data of the contact pins; wherein said second memory unit stores the positional pattern data of the contact pins.
The IC package testing device of the present invention may comprises: a plurality of pilot pins which are provided in the socket and have a fixed positional relationship with the contact pins; and a socket calibration jig including a plurality of pilot holes which are fitted around the pilot pins and a plurality of image recognition marks which have a fixed positional relationship with the pilot holes; wherein said camera unit images the image recognition marks, said image recognition unit recognizes an image of the image recognition marks, processes the image, and obtains a positional data of the image recognition marks and the positional pattern data of the contact pins, and said second memory unit stores the positional pattern data of the contact pins.
Said adjusting unit may include a chuck unit which transfers the IC package along the X-axis and the Y-axis and rotates the IC package in a horizontal plane.
A difference between an inner diameter of each of the pilot holes and an outer diameter of each of the pilot pins may be equal to or less than 0.01 mm.
The unit for holding the IC package in the carrier unit may comprises a suction device including a suction surface for sucking onto the IC package.
The carrier unit may comprises: a motor for raising and lowering the IC package; and a load cell for measuring a load on the IC package, wherein an operation of the motor is controlled in association with the load on the IC package which is measured by the load cell. In this case, a plurality of the load cells may be disposed on the same plate provided parallel to the suction surface.
Thus, the load applied upon abutting the solder balls respectively on the contact pins can be constantly and optimally controlled, thereby minimizing the electrical resistance at the point of contact and improving the accuracy of the measurement for the electrical characteristics of the IC package.
A method for testing an IC package according the present invention comprises: imaging and recognizing a positional pattern of the solder balls in the IC package, storing said positional pattern data of the solder balls in the IC package; storing a positional pattern data of the contact pins in the socket; adjusting a position of the IC package so as to align the positional pattern of the solder balls with the positional pattern of the contact pins at a positioning section; carrying the IC package to the socket and contacts the solder balls to the contact pins by a carrier unit; and measuring electrical characteristics of the IC package after contacting the solder balls on the contact pins while holding the IC package by the carrier unit.
The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals.